This invention relates to laminates of plastics, metals, or glass. More particularly, this invention relates to multilayer laminates of plastics, metals, or glass, wherein the laminates contain an addition-curable silicone adhesive composition between the layers of the laminate.
Multilayer laminates containing plastic, metal, or glass substrates have many uses in the marketplace. One particularly important application is in flexible circuits containing multilayer laminates of bonded polyimide or polyester film and copper or aluminum foil. Current flexible circuit processing is all manual and requires extensive press-cure times for manufacture. The projected high growth of the flexible circuit market is critically limited by the high labor assembly costs and the lack of processing speed. It is continually desirable, therefore, to discover ways to increase the speed of producing the flexible circuits.
Generally, an adhesive composition is used to bind the layers in a multilayer laminate. There are several critical properties necessary for an adhesive composition to be useful in high productivity lamination processing. Among these are fast cure, high peel strength, excellent thermal-dimensional stability, and innerlayer stress-management capability. In addition, such compositions must be solventless and able to bond directly to plastic, glass, and metal substrates, i.e., without the use of primer between the adhesive composition and the substrate.
Adhesives presently used in flexible circuit laminates include reactive epoxies, modified epoxies, acrylics, polyesters, and thermoplastic adhesives such as fluoroethylenepropylene. These adhesives do not have all of the properties recited above as critical to the effective performance of an adhesive in high productivity lamination processes.
Thus, it is continually desirable to provide a multilayer laminate of plastic, metal or glass, wherein the laminate contains an improved adhesive, wherein the adhesive does not require solvent or primer, has high peel strength, excellent thermal-dimensional stability, and innerlayer stress-management capability.
The present invention is directed to multilayer laminates containing at least 2 substrates selected from various plastic, metal or glass materials, and containg a solventless, addition-curable silicone adhesive composition which contains an adhesion promoter selected from certain silylfumarates, silylmaleates, or silylmaleimide compounds and which cure to form superior adhesives having excellent physical and adhesive properties and which will adhere to various substrates without the use of a primer and which also has the other properties recited above as necessary to make it an effective adhesive in the manufacture of industrial laminates of plastic, metal, or glass, e.g., flexible circuits.
The use of silylfumarate and silylmaleate compounds as adhesion promoters in silicone compositions is known in the art. Reference is made, for example, to U.S. Pat. Nos. 3,941,741 (De Zuba et al.), which discloses the use of a maleate, fumarate, silylmaleate, or silylfumarate compound as a self-bonding additive in a heat-curable silicone rubber composition. Reference is further made to U.S. Pat. No. 4,273,698 (Smith, Jr. et al.); U.S. Pat. No. 4,308,372 (Smith, Jr. et al.); and U.S. Pat. No. 4,395,507 (Dziark et al.), which disclose the use of a silyl maleate, a silyl fumarate, or a silyl succinate as an adhesion promoter in room temperature curable silicone compositions.
The use of silylfumarate and silylmaleate compounds as adhesion promoters in addition-curable silicone compositions is also known in the art. Reference is made, for example, to U.S. Pat. No. 4,891,407 (Mitchell).
U.S. Pat. No. 4,891,407 to Mitchell is directed to a composition having interpenetrating matrices containing two polymer networks. The first is any polymer that is capable of being stretched, drawn, or expanded so as to obtain a microstructure characterized by nodes interconnected by very small fibrils and is preferably polytetrafluoroethylene. The second polymer network can be an addition curable silicone composition containing an alkenyl-containing polydiorganosiloxane, an organohydrogenpolysiloxane, an organic peroxide or a precious metal-containing catalyst, and, optionally, a reinforcing organopolysiloxane resin, extending and/or reinforcing fillers. The addition-curable composition preferably further contains an adhesion promoter which Mitchell discloses can be any of the maleate and fumarate-functional silanes disclosed in U.S. Pat. No. 3,759,968 to Berger et al. , which can be a silylmaleate or silylfumarate, such as bis[3-(trimethoxysilyl)-propyl]maleate or bis[3-(trimethoxysilyl)propyl]fumarate.